Thanks for the tip, Glenn.  I had spoken with several jet-experts, and none if the leads gave me an answer about a smaller UHMW foot.  The company that used to make them stopped because a sheet of that stuff costs about $15k.  I hope Rockproof makes one that will fit.
I've heard it said, in these rocky ledge filled rivers, if you don't destroy a few lower units, you're not "really" jet boating.  I hope the UHMW will be the ticket.
I'm Off to the New River!